IEC 61557-5:2007

Overview

IEC 61557-5:2007 is an international standard developed by the International Electrotechnical Commission (IEC). It is part of the IEC 61557 series addressing electrical safety in low voltage distribution systems up to 1,000 V a.c. and 1,500 V d.c.. Specifically, Part 5 focuses on the requirements for equipment intended to measure earth resistance using an a.c. voltage. Earth resistance testing is essential to ensure the effectiveness of grounding systems as a protective measure, helping to safeguard people and property from electrical faults.

This second edition of IEC 61557-5 incorporates a complete revision of definitions and refinement of several requirements compared to the previous edition.

Key Topics

• Scope and Application: IEC 61557-5 applies to devices measuring earth resistance with alternating current in low voltage installations, which are crucial for confirming safety and compliance within distribution networks.
• Definitions: The standard defines critical terms such as series interference voltage, auxiliary earth electrode, probe, and probe resistance, ensuring a common understanding for manufacturers and users.
• Performance Requirements:
  • Output voltage must be a.c., free from a d.c. component
  • Equipment must mitigate the influence of external electrical interference
  • The marked or stated operating uncertainty of measurement must not exceed ±30% within its specified range
• Safety: Protection against hazardous touch voltages is mandatory, achieved through design features such as voltage and current limitation or automatic disconnection under fault conditions.
• Marking and Instructions:
  • Equipment must be clearly marked with measurement range, output voltage frequency, and terminal designations
  • Operating instructions should specify the intended application, highlight potential sources of error (such as interference voltages), and provide necessary operational details for correct and safe measurement
• Testing: In addition to type and routine tests specified in IEC 61557-1, IEC 61557-5 stipulates procedures to verify:
  • Measurement uncertainty limits
  • Compliance with voltage and current safety thresholds
  • Functionality of overload protection mechanisms

Applications

IEC 61557-5:2007 is highly relevant to:

• Electrical contractors and installers: Ensures proper grounding in new and existing installations
• Maintenance professionals: Regular testing of earth resistance for ongoing electrical system safety
• Manufacturers of earth resistance measurement equipment: Provides clear benchmarks for design, safety, and performance validation
• Compliance inspectors and auditors: Reference for verifying that low voltage distribution systems fulfill international safety requirements

Practical application examples include:

• Assessing earthing effectiveness in residential, commercial, and industrial electrical systems
• Earth resistance measurement in agricultural plants, where stricter voltage safety limits may apply
• Verification of grounding systems ahead of commissioning or after modifications to electrical installations

Related Standards

• IEC 61557-1: General requirements for equipment for testing, measuring, or monitoring of protective measures in low voltage distribution systems (must be used in conjunction with Part 5)
• IEC 61010-1: Safety requirements for electrical equipment for measurement, control, and laboratory use
• Other parts of IEC 61557 series: Cover requirements for equipment measuring insulation resistance, loop impedance, and other protective measures, providing a comprehensive framework for electrical safety testing in low voltage systems

IEC 61557-5 supports globally consistent practices for electrical safety in low voltage installations. Adhering to this standard enhances protection for people and equipment, supports regulatory compliance, and promotes confidence in electrical infrastructure worldwide.